class_docstr: A Concept class, loosely based on SKOS
  (https://www.w3.org/TR/swbp-skos-core-guide/).
code: def __repr__(self):
      return "Concept('%s')" % self.prefLabel
  
imports: import os
  import re
  import shelve
  import sys
  import nltk.data
label_desc: Use image node_id 3 for calling the Concept obj's underlying member method code with example usage: obj.__repr__() and returns: unknown